The present invention relates to cross-over relief valve assemblies, and more particularly, to such valve assemblies for use in “bi-directional” circuits, i.e., circuits in which either side of the circuit may comprise the high pressure side, and either side of the circuit may comprise the low pressure side.
As is now well known to those skilled in the art, the function of a cross-over relief valve assembly is to protect a hydraulic circuit, and the various hydraulic components which comprise the circuit, from excessive pressure spikes or pulses which may, periodically, be present on the high pressure side of the circuit. Such protection of the circuit is achieved by providing a cross-over relief valve assembly which is designed to relieve (drain) the excessive pressure from the high pressure side of the circuit to the low pressure side of the circuit, whenever the fluid pressure in the high pressure side of the circuit exceeds a predetermined, pressure relief setting.
Although the cross-over relief valve assembly of the present invention may be utilized advantageously in many different types of hydraulic circuits and with many different types of fluid pressure operated devices, the invention is especially advantageous when utilized in a closed-loop hydrostatic circuit, including a hydraulic motor, and the invention will be described in connection therewith. Furthermore, the cross-over relief valve assembly of the present invention is especially beneficial when utilized in a hydrostatic circuit in which each side of the hydrostatic loop may switch fairly frequently between high pressure and low pressure.
In certain, prior art, cross-over relief valve arrangements, there has been provided a relief poppet having approximately half of its area subjected to the fluid pressure in the “A” side of the loop, and the remainder of its area subjected to the “B” side of the loop. In such an arrangement, if either side of the loop (“A” or “B”) exceeds the predetermined pressure relief setting, the poppet would open and relieve fluid to the other (low pressure) side of the loop. However, the above-described arrangement is based on the assumption that the low pressure side of the loop will always remain at substantially zero pressure (i.e., reservoir pressure). If the hydrostatic loop in which the above-described arrangement is being utilized is subjected to a back pressure (i.e., a pressure above atmospheric on the low pressure side of the loop), such an elevated “low pressure” will assist the system high pressure in biasing the relief poppet toward an open position, thus effectively reducing the pressure relief setting and causing the cross-over relief valve to open at a pressure less than the predetermined, maximum relief setting.
Also, it has been common in hydrostatic circuits utilizing a motor to provide a pair of fairly conventional cross-over relief valves, one being operable to communicate the “A” side of the loop to the “B” side, and the other being operable to communicate the “B” side of the loop to the “A” side. Although such a dual cross-over relief valve arrangement is functionally acceptable, the addition of one more expensive relief valve can make the overall hydrostatic circuit economically undesirable. The duplication of relief valve assemblies can also complicate the packaging of the circuit.